R. A. Heising of AT&T contributed a paper to Journal of the Franklin
Institute vol. 193, no. 1, January 1922, p. 97 titled ”Printing
Telegraph by Radio.” This presents the results of AT&T experiments
transmitting between New York City and Cliffwood, New Jersey, a distance
of 25 miles. The experiments were done in 1919, using a wavelength of 450
meters (666 KHz). The operating speed was 180 wpm, using a four-channel
time-division multiplex at 45 wpm per channel. He noted that the principal
source of interference in NYC came from spark transmitters.

Federal Telegraph Co. conducted experiments on the West Coast USA circa
1920 using frequencies in the 35-70 KHz range. [RTTY Magazine, April,
1955, p. 7.] Their transmitter used a Poulsen arc, and therefore was
frequency shifted rather than keyed on and off; however no use was made of
the properties of FSK. It was simply too hard to key the arc on and off.
The path was between Hillsboro, OR and the KFS site near San Francisco.
The test results were not sufficiently good to recommend the system for
revenue service.

These patents are assigned to the Morkrum Co.; however Brady’s residence
is given as Somerset, Maryland so he must not have been a regular
employee of Morkrum. All of these patents cover make-and-break keying of
the transmitter. In the first of these he says that the system has been
successfully operated between the U.S. Naval Aircraft Radio Laboratory at
Anacostia, D.C. and the U. S. Naval Radio Research Laboratory, Bureau of
Standards, Washington, D.C. Points stressed in the first patent are:

• Use of printing telegraphy, not requiring skilled operators
• System is ”substantially” secret in that signals cannot be copied
by ear
• Code can be changed from time to time for increased secrecy.

The illustrations show a vacuum tube transmitter grid-block keyed by a
relay connected to the keyboard contacts. The receiver has a regenerative
detector followed by two stages of audio amplification. The final stage is
tuned to a particular audio frequency, which is then applied to two
paralleled triodes operating a relay in the printer circuit. An odd item
is a series tuned circuit shunting the relay, with a switch to disconnect
it. There is an illustration of a tape strip printer with a typewheel
inside. He gives a hand-waving description of the Morkrum machine. He
shows what look like single-magnet selector magnet coils, but doesn’t
show what goes on between these coils and the rest of the machine; so it
is not clear whether this is a machine with a single-magnet selector. The
coils are identified as ”teletype coils”, showing that the word
”teletype” was in use at this early date.

Patent 1,523,377 shows a
system in which teleprinter signals are transmitted by radio to any of a
number of receiving printers. Circuits are shown for both make-and-break
keyed transmitters and transmitters modulated with audio tones. A
principal feature of this patent is use of signals at one frequency to
transmit the intelligence and signals at a slightly different frequency to
control the motors of the receiving printers. With the make and-break
transmitter the start-stop keyboard key is arranged to change the
transmitter frequency slightly. With the audio modulated transmitter the
tones are generated by buzzers at two different frequencies, one for the
message signals and the other for motor control. Hence the receiver may or
may not need a heterodyne oscillator to produce an audio signal from what
it receives.

The receiver employs a
sharply-tuned filter to detect the motor control frequency. The motor
control detector drives a plunger-type solenoid relay which reverses each
time it is energized, so that one signal turns the motor on and a second
signal at the same frequency turns it off. The speed-governed motor uses
electron tubes in its control circuit, the subject of another patent
applied for by the same inventor. Presumably this is to reduce the RF
noise generated by the motor governor. The message-signal-frequency
channel of the receiver operates a relay which controls the teleprinter
receiving magnet.

Points stressed are:
• One transmitter to any number of receiving stations
• Automatic (suggesting unattended) reception
• Motor control of receivers
• Selecting some groups of receivers to receive to the exclusion of
others

The keyboard in the illustration looks something like a Model 14. The
printer is not shown.

Patent 1,562,820 improves upon 1,563,958 by using an AC-powered receiver
instead of a battery model. Power for the Teletype selector magnet is
obtained from the same AC supply, as is power for the printer motor. He
notes that AC-powered printer motors generate a lot of RF noise and that
DC motors are superior in that respect; but you can run the motor off AC
if you want to.

He says the application
is receiving news from a central radio station, stresses the simplicity
and compactness of the arrangement for installation in business houses,
banks, between warehouses and large stores. Suggests use of very high
frequencies (10 meters) allowing directional antennas and confining the
transmissions to a particular area. ”Teletype” is capitalized.

Patent 1,563,958
shows radio receiver including a tone detector driving a relay which
operates a Teletype printer. It goes into some detail about the selector
mechanism.

The Navy also did some
experiments in air-to-ground radioteletype, documented in Scientific
American, March 1923, p. 173. The illustration shows something like a
Model 12 keyboard in the airplane and a Model 11 tape printer on the
ground. The article states that the next experiment would be transmission
from ground to air. The Bureau of Standards was also involved in this
work, and perhaps Mr. Brady.

1,705,211:
This appears to be the original concept of frequency-shift-keyed
radio-teletype operation. It shows teleprinter sending contacts, or a
relay, connected to a radio frequency oscillator-transmitter to shift the
frequency slightly. Another circuit shows an audio frequency shift keyed
oscillator modulating a radio transmitter. The receiver has a pair of
audio tuned circuits, one tuned to mark and one to space frequency, each
feeding a triode detector that drives one winding of a polar relay. A
differential milliammeter allows for accurate adjustment to eliminate
bias. The inventor explains why his system is superior to make-and-break
operation for teleprinter use in terms of not having the inertia inherent
in a neutral relay. He also refers to radio transmitters used for Morse
and having a ”compensating wave”. These were transmitters which were
frequency-shift keyed because that was easier than make-andbreak; but the
compensating wave (space) was not desired and was ignored. Indeed it had
to be placed at a frequency far enough away from the intended carrier to
enable it to be ignored. He proposes a shift of 250 Hz with spacing lower
than marking frequency as an example, with a marking frequency of 230.50
KHz. The patent also mentions the possibility of a two-channel multiplex,
although the exposition of this idea is not very clear. (Presumably it
applies to amplitude modulating two audio FSK signals on a single radio
frequency carrier, as there is no suggestion of the logic required to
operate a transmitter shifting among four radio frequencies.)

2,012,407:
This is said to be an improvement on 1,705,211 above. More accurately it
is an adaptation of that system for use with make-and-break keying. A
shunt, consisting of a variable resistor in series with an inductor, is
placed to produce a marking bias current through the relay equal to half
the current when a spacing signal is being received. The space filter is
tuned to the signal frequency, and the mark filter is tuned to a nearby
frequency. The assertion is that static and noise will be received equally
in both channels and will cancel out. This is aided by the inductor in the
shunt circuit, which makes the shunt ineffective on transients so that
they affect both windings of the polar relay equally.

A recent article by Mischa Schwartz of Columbia University [published in
Antenna, the newsletter of the Mercurians, a sub-group of the Society for
the History of Technology, October 2007] calls attention to a paper by
Armstrong, ”Methods of Reducing the Effect of Atmospheric
Disturbances”, Proceedings of the I.R.E., January 1928, p. 15 (with
discussion on p. 27). In this paper Armstrong proposed something very
similar to Schmitt’s patent - use of separate marking and spacing
frequencies for telegraphy, and subtracting outputs from the two
detectors. Like Schmitt, Armstrong makes the intuitive assumption that
noise will affect both frequencies more or less equally and cancel out
when the signals are subtracted. Note that in this application Armstrong
was not yet using a limiter ahead of the mark and space filters, so that
it is not true FM as he developed later. Schwartz then references a paper
by Carson of AT&T, ”The Reduction of Atmospheric Disturbances”,
Proceedings of the I.R.E., July 1928, p. 966. in which Carson argues that
Armstrong’s scheme is not effective in canceling noise. Yet Armstrong
had supplied ink recordings showing the superiority of two-tone operation.
It seems that for a fair comparison the two-tone scheme should be compared
with make-and-break transmission at twice the power, because of the 100%
duty cycle of two-tone versus the approximately 50% duty cycle of makeand-break.
Carson indeed suggested that an advantage might be had by transmitting the
message twice so as to use the same power as the FSK proposal. I’m not
clear whether he meant to transmit two copies on two different
frequencies, or on the same frequency at two different times. He does note
that the FSK transmission involves twice the receiver bandwidth of the
single-channel transmission.

It seems to me that Carson’s critique of Armstrong’s proposal needs to
be tempered by instrumental considerations. Copying Morse code signals by
ear makes use of the operator’s training and the marvelously complex
human auditory system to separate the signal from the noise. Copying with
an ink recorder bypasses all that with a fairly simple electronic circuit,
but still preserves some of the analog nature of the signal. Operator
skills still come into play, in a reduced way. For reception by automatic
printer the incoming signal must operate a relay, which eliminates all
human ability from the process and substitutes simple electronics. FSK may
be a greater help in this situation that is apparent from theoretical
considerations of signal to noise ratio. The relay transitions in one
direction when the marking channel signal exceeds the spacing channel
signal, and in the opposite direction when the opposite signal conditions
are true. With make-and-break keying the relay has to be biased somewhere
between the noise level and the expected signal level.

It seems unlikely that
Schmitt and Armstrong were aware of each other’s work. The main point of
Schwartz’s article is that Armstrong went on to employ a limiter; and by
that means the noise-reduction ability of FM was realized.

The radio receiver is shown only as a block. An A.C. power supply is
shown; and the printer is shown as having an A.C. motor. Like Brady, he
suggests ”there may be a demand for a radio printer service in which the
news matter would be broadcast from a central transmitting station to the
newspapers subscribing for such service.” Make-and-break operation is
used. The detector tube operates a polar relay which drives the printer
magnets - a polar printer magnet is shown. An extra winding of the polar
relay is connected to the secondary of a ”kick” transformer, the
primary of which is in series with the operate winding of the polar relay.
This is intended to insure quick operation of the polar relay.

The radio equipment is
shown only in block form. The essence of the invention is to transmit each
character three times, from a rotary distributor having three sets of
segments. A character received the same all three times will be printed.
If the character is not received the same all three times only the marking
pulses which agree will appear in the printed character. ”It is well
known that static can only cause marking pulses...” which shows that he
is talking about make-and-break keying; for with FSK static would affect
marks and spaces more or less equally. A lot of relays are used at both
transmitter and receiver.

Austin Bailey and T. A. McCann of AT&T contributed a paper to Bell
System Technical Journal vol. 10, October 1931, p. 601, ”Application of
Printing Telegraph to Long-Wave Radio Circuits.” This was a paper
presented at the 6th annual convention of Institute of Radio Engineers.
Notes the need for better signal-to-noise ratio for printing telegraphy
compared with aural Morse operation. It cites advantage of two-tone
operation over single-tone. As with the Schmitt patent, two-tone operation
is analogous to polar operation of a wire circuit in preventing bias
resulting from varying signal strength. Discusses experiments conducted on
a 60KHz carrier circuit between New York and London, using a power of
50KW. Directive antenna systems helped to combat noise. Further tests were
conducted in 1930 between Rocky Point, Long Island, and Rochester, NY, a
distance of 286 miles. Power was 700 watts.

I have a picture of the Morkrum plant site, 1400 Wrightwood Ave., Chicago,
when part of it was a vacant lot. This shows some antennas being erected
for radioteletype tests with Lake Geneva, Wisconsin. The word from Walt
Zenner, by way of Bob Reek, is that there were radio experiments between
the Morkrum plant and Sterling Morton’s home in the western suburbs of
Chicago. Also that when Walt arrived at Teletype, Schmitt was the plant
engineer, responsible for utilities and the like. Nothing came of his
radio work. I presume that when Teletype was an independent company it was
scrambling for business wherever it could be found. After the purchase by
AT&T it was viewed as an equipment manufacturer; matters involving
transmission were on AT&T and later Bell Labs’ turf.

It was reported in
Telegraph and Telephone Age, October 1, 1932 that RCA Communications Inc.
was using radioteletype between San Francisco and Hawaii, with plans to
extend the use of RTTY in the immediate future.

A paper by Moore of RCA [Accuracy and Speed on Short-Wave Teleprinter
Services; John B. Moore; Proceedings of the National Electronics
Conference, Chicago, 1953, pp 927-934] confirms the use of radioteletype
on the San Francisco to Hawaii Circuit and notes that it was not possible
to use radioteletype on the Atlantic circuits at that time. Morse
operation was faster, up to 300 words per minute versus 60. Time- division
multiplex was employed starting about 1935 to allow teleprinter operation
to compete with Morse. An error-detecting code was developed and used from
1939 until 1947. Post World War II a system called ARQ (automatic request
for retransmission) was developed, based on the error detecting code. With
this system a receiving station detecting an error in incoming traffic
signals the sending station to retransmit the text that was received in
error. Systems based on this principle continue in use today: for example
the SITOR system used in marine communications. With microcomputers it is
extremely simple to implement such a system.

Moore goes on to note
the increased need for record communication by radio during World War II,
met by frequency-division multiplexing over single sideband radiotelephone
circuits, and the development of frequency shift keying. RCA developed a
two-channel time-division multiplex that was more tolerant of signal
distortion than a single-channel teleprinter.

Press Wireless, Inc. was
also active in exploiting frequency shift keying for teleprinter operation
over radio. A paper [Frequency Shift Radiotelegraph and Teletype System;
Robert M. Sprague; Electronics, Nov. 1944, pp. 126131] notes that
company’s use of FM for facsimile transmission followed by the use of
FSK for telegraph transmission. This article shows that a limiter discriminator
scheme was in use. Hence performance in the presence of noise and
interference is governed by FM principles rather than by those of
limiterless two-tone systems. He notes the adoption of 850 Hz as the
standard for frequency shift, saying that gives the best compromise
between signal to-noise ratio and bandwidth. There is some discussion of
the bandwidth requirement of make-and-break keying, which is
considerably greater than than the theoretical requirement because of
squaring of the waveform in the transmitter. I suspect that such a wide
shift as 850 Hz was also helpful in coping with frequency drift of
transmitters and receivers in that era. This conjecture is supported by
their use of A-C coupling between the discriminator and the loop keyer,
with a threshold correcting circuit in between.

Probably the best known RTTY equipment of World War II is the AN/FGC-1
diversity FSK converter and its companion AN/FRR-3 diversity
receiver. These units were manufactured by Western Electric using typical
telephone style construction, apparatus mounted on flat plates, each unit
occupying a 7-foot rack cabinet. Hence the units are largely for
fixed-station use and on fixed frequencies. The Navy had some RTTY
demodulators operating at the receiver intermediate frequency rather than
at audio frequency.

Use of RTTY in amateur radio seems to have begin in the late 1940s in the
New York City area. The reason seems to have been a confluence of amateurs
having knowledge of military radioteletype during World War II and the
availability of teleprinters. The New York Police Department had a network
of Model 12 machines, which they had to replace because maintenance
parts were no longer available. News wire services were disposing of their
Model
12 machines for the same reason. Amateurs were able to acquire these
antiquated machines. They were put into operation on 2 meters using AFSK.
The main reason was that FSK was not authorized for amateurs on the HF
bands. A secondary reason was that the Model 12 was a prodigious generator
of RF noise that made HF reception extremely difficult. Amateurs
trying to operate Model 12 machines on HF resorted to measures such as
vacuum tube keying of the code magnets and the governed motors.

For some reason, in
spite of the huge amounts of radio equipment sold as war surplus, there
was hardly any Teletype equipment. Perhaps the U.S. military needed to
retain all its teleprinters as it phased out Morse operation; perhaps
foreign governments outbid the surplus dealers; perhaps the surplus
dealers just didn’t imagine any market for Teletype equipment. The New
York hams did have access to a trickle of Western Union surplus, little of
which was readily usable.

The New York area
operators tended to run high power on VHF. Perhaps there was some scatter
propagation augmenting line-of-sight. John Williams W2BFD designed an AFSK
converter that was duplicated by a number of the New York hams. Another
feature of the New York area operation was timed autostart. Stations would
arrange to have their equipment turned on for a few minutes at the
beginning of certain hours, under control of clocks. During that time they
could receive messages unattended.

There was some
experimentation on HF using make-and-break keying. FSK was allowed only on
the 11-meter band until 1953, when privileges were extended to the CW-only
portions of all the HF bands. Shift of 850 Hz and speed of 45.45 baud were
required by the FCC rules.

Amateur RTTY suffered indifference, if not hostility, from ARRL. One
reason was the bandwidth occupied if FSK were to be used. Why occupy
nearly a kilohertz (using the required 850 Hz frequency shift) to transmit
at 60 wpm when CW could operate almost as fast (assuming a skilled and
talented operator) in a lot less bandwidth? The CW operators didn’t
appreciate having their band segments occupied by the relatively wide RTTY
signals. Another reason I think was that ARRL discouraged the use of any
technology that the amateur could not build himself; that certainly
included a teleprinter. In the same vein ARRL tended to ignore military
surplus equipment. There was the official QST advertising policy that
everything offered had to be new manufacture, not used or surplus. This
situation did not change until RTTY achieved a considerable degree of
popularity and ARRL member hams began to demand more coverage in QST. (And
perhaps until some of the older ARRL officials had retired.)

In the absence of much
information in the ARRL official journal QST, most of the published
information available to amateurs came through other channels.

• The publications of Amateur Radio Teletype Society, also known as
V.H.F. Teletype Society, of the New York area.
• RTTY, the journal of the Southern California RTTY Society.
• A RTTY column in the magazine CQ, first written by Wayne Green W2NSD.
Wayne was also for a time editor of the ARTS bulletin. Later he became
editor of CQ and the RTTY column was taken over by Byron Kretzman W2JTP.

The ARTS publications came out rather irregularly and seemed to just fade
away as time went on. RTTY ran from 1953 through 1966 as a labor of love
of Merrill Swan W6AEE. Then it was sold to a more commercial publisher and
continued into the late 1990s under various publishers. By then there were
other digital modes in use; and RTTY operation was usually fully
electronic rather than using a mechanical teleprinter. RTTY articles in CQ
continued until 1965 or so. QST began giving major emphasis to RTTY about
that time as a result of demands from the membership.

There was also personal contact, through organizations and one-on-one
meetings, of RTTY-savvy amateurs with those wishing to get started. Nearly every
large population center had an RTTY society in its area.

As noted earlier, the first teleprinters used by amateurs were primarily
the obsolete Model 12 machines, and an assortment of other oddities. The
telephone companies had a policy of destroying any machines surplus to
their needs, to prevent their being used in competition with their charged for
services. Amateur organizations entered into protracted negotiations with
AT&T and its subsidiaries and eventually achieved agreements that
surplus machines could be sold to amateurs. These sales all required that
the buyer sign a waiver of any non-amateur use for the machine. In the mid
1950s the telephone companies began releasing quite a few Model 26
machines. These were page machines originally used in Bell’s TWX
service. They were made in the late 1930s in an attempt to have a
lower-cost light-duty machine that could replace the heavy-duty Model 15
in TWX service. The expected economies were not achieved; so after World
War II AT&T decided that Teletype could quit supporting them with
maintenance parts and that they would be phased out of service. A trickle
of Model 15 machines came into amateur hands as well. Well-heeled amateurs
could obtain the latest Model 28 machines, the new Bell System and
industry standard, principally for individuals who refurbished them from
junked equipment. One prominent refurbisher was Ray Morrison, W9GRW. Later
there was Model 28 equipment being surplused by the telephone companies,
probably as a result of the transition to ASCII equipment.

The standard commercial and military method of generating FSK signals
through the 1940s and 1950s was to use a 200 KHz L-C oscillator with
reactance tube modulation to vary the frequency. The desired output
frequency was obtained by heterodying a crystal oscillator with the 200
KHz oscillator, and in some cases by frequency multiplication from a lower
frequency. This method of modulation was fairly linear, so the equipment
could be used for FM facsimile transmissions as well as for FSK. Amateurs
used a much simpler arrangement, a diode which could be biased on or off
to switch a slight reactance into a variable frequency or crystal
oscillator to shift its frequency. Varying the bias allowed varying the
shift, albeit not linearly.

The standard commercial,
military and amateur method of receiving FSK signals through the early
1960s was the FM limiter-discriminator circuit, followed by a trigger
circuit to provide solid mark and space signals to the teleprinter or
other equipment. Unfortunately the usual amateur designs were somewhat
faulty, based on some misunderstandings of filtering. Don Wiggins W4EHU, a
professor at University of Florida, attempted to set things right with
articles in RTTY in 1960 and 1963. He explained why any narrow filtering
needed to go ahead of the limiter, and why the discriminator should be
linear far beyond the mark and space frequencies. Sprague had stated this
principle in his 1944 article but did not explain the reasoning behind
it.

Some Post Office workers
in England published a paper in 1957 on non-FM detection of FSK signals,
treating mark and space as a frequency diversity pair of on-off keyed
signals. In a sense this was a reversion to the early ideas of Armstrong
and Schmitt, but with more involved ways of combining the two signals. An
amateur terminal unit without a limiter had been described by Gates in
RTTY in 1954, but had attracted little attention. The idea hit the amateur
community in full force about 1963. Thereafter it found its way into FSK
converters designed mostly by amateurs but marketed to commercial and
government customers.

As electronic technology has advanced so spectacularly in recent years the
mechanical teleprinters have fallen by the wayside, except for nostalgia
reasons. First we had active filters and video terminals based on personal
computers. Then came digital signal processing on specialized DSP engines;
and then personal computers became powerful enough to do digital signal
processing without extra hardware on the side. New modulation methods are
continually being invented, all offering some improvement over two-tone
FSK. Baudot RTTY continues to be used in amateur radio, but only in two
niches: contesting and DX (distant station) chasing. For other purposes
the newer modulation methods generally offer much better performance than
RTTY.

Disclaimer: The above is not the result of an exhaustive search of patents
and literature pertaining to radioteletype. Rather it is material I ran
across
while searching for other things. The above should be considered a work-in
progress. J.H.

Editors note - How sad there model 12s stacked up
like cordwood at one time and now nary one to be
found. SMECC DESPERATELY needs any model 10, 11 or
12 teletype gear for our corner of the
display that ... alas just hold a photo on one
presently!

Although ARRL did not publish as much on Radio Teletype as
many of the other publications did (as noted by Jim Haynes in the
above article) John Evans Williams had an early QST article on Radio
teletype history you can read HERE

WANTED! More info and photos of this
early era!
Please Email Ed Sharpe Archivist for SMECC at
info@smecc.org

HAL HISTORYHAL Devices - HAL Communications Corp.

By Bill Henry,
President HAL Communications - Retired

HAL history goes back to 1966/67. We started as
"HAL Devices", a partnership, but formalized in 1972 as
"HAL Communications Corp.", an Illinois Corporation. From the
start we were hams and graduate students at the University of Illinois In
Urbana. Until last year, HAL was owned by one or more of the original
founders.

The name "HAL" was chosen by the first HAL
Devices partner, George Perrine. George said he picked the name because it
is "one letter ahead of IBM". Turned out to be a good choice and
easy to remember. It also does not seem to have any "nasty
translations" into any other language. There was not and never has
been any connection to "Hal", Arthur Clarke's intelligent
computer in the screen play "2001" - later published as a book.
We were very surprised when the movie hit the Coed Theatre on campus and
discovered that the movie's computer had our name. We never had any
problems with that similarity - "Hal" for the movie and
"HAL" (all caps) for our small company. But, from time-to-time,
we did have issues with others trying to use "HAL". That
resulted in us paying lawyers. The offenders folded or eventually went out
of business. I've also had issue with others reprinting several of my
technical articles under their own names. I am sensitive to that and over
the years paid a lot of money to attorneys to protect HAL's documents.

HAL Devices:

HAL Devices started in 1966 as a loose partnership of
3, 4, or 5 graduate students at the University of Illinois in Urbana,
Illinois. We bought parts from various sources and then resold them at
hamfests. The big items were the Fairchild 900 RTL chips - 8 pin round
plastic packages. We bought ours in 100 lots from Semiconductor
Specialists in Chicago and then resold them at hamfests for a price midway
between list and the 100-lot price. Our first "product" was a
double-balanced modulator circuit board that used HP hot carrier diodes.
That was based on an article in Ham Radio Magazine. We also sold CW keyers
- the 111/211/311 Keyer, then the 1550, and finally the 2550. The numbers
used to mean something but I have no recall now. My activity started with
the RT-1 TU that I designed for use on USAF MARS. It worked but was not
manufacturable or easily serviced - live and learn. The ST-6 was of course
our first big deal product and it continued for almost 10 years. The RVD-series
of video display generators put us on the map. Terminal products continued
to dominate sales well into the 1980's - until the IBM-PC and its clones
came along. HAL Devices evolved as our products and customer base
increased. Our "facilities" included George Perrine's unheated
garage, my basement, Paul Tucker's kitchen, and finally 2000 sq. ft. on
Locust Street in Champaign. Jim McNabb, WA9YLB, was our first full-time
employee, complete with a paycheck, payroll deductions, and all that
stuff. The assemblers still did piece-work but now had a place to work
other than their kitchens or basements. We soon hired several high-school
students to help with bagging parts, packing orders, and testing of
equipment.

HAL Communications Corp.:

On January 1st, 1972, George Perrine, Paul Tucker,
and I met at in Champaign to discuss the future. The meeting started at
8AM and lasted until NOON the following day, 1/2/1972. With pizza, donuts,
Big Mac's and many pots of coffee, we hammered out the organization that
became HAL Communications Corp. As a result of the meeting, HAL Devices
was sold to HAL Communications Corp. with each of us receiving equal
shares in the new company. HAL Communications quickly out-grew the 2000
sq. ft. facility in Champaign and in 1973, we purchased an old grocery
store building in Urbana. That building served us well until we built the
present facility on Kenyon Road in 1980. In July, 1976, George Perrine
moved on and Paul and I purchased his interests. In 1983, Paul also moved
on and I became the sole stockholder and owner. On Dec. 7, 2012, I sold my
stock and interest in the company to Barrett Communications in Perth
Australia. Joe Wittmer (my son-in-law) continues as Managing Director for
Barrett.

That's the short form of the "history". The
list of products is long - several hundred, I think. Some were successful,
many were not. We had some really great ideas - like the video display
generator, ASR terminal, MSO (mailbox), fancy modems, and of course
CLOVER. Other ideas were not so great! You win some and you lose some. I
had a flirtation with doing MIL-SPEC products and for 5 or 6 years it was
very successful and profitable. But I almost lost my shirt when a big
contract was suddenly dropped. Learned my lesson - never bid on another
government contract after that (1995). Over the years, I counted over 300
different names in my employee files. Two people who started with us in
1972 are still there - Phyllis Costa, Assembler, and Mark Prather,
Manufacturing Manager. As I mentioned above, Joe Wittmer continues as
General Manager. None of us at HAL ever had much money. The company was
always "leveraged" - heavily leveraged in some years. Growth
depended on selling something. I was approached by "investors"
and venture capitalists but never accepted their money - or control. I
witnessed several friends go through that with generally bad results. We
did make use of bank loans but that became increasingly difficult after
1993. The best plan for a small business is to not spend any more than you
have! (Easy to say now.)

I thoroughly enjoyed the job. There are not many
occupations where you get to pay yourself to do exactly what you always
wanted to do. I had never planned to retire - "I'll die at my
desk" was my response when asked. BUT - Barrett came up with "an
offer I couldn't refuse" and here I am. In hindsight, I see that I
should have planned for this. I really miss the place.
"Retirement" is OK but gets boring at times. I still wake up in
the wee hours worrying about business things - like I had done most
mornings for the last 45 years. "Getting old is not for the faint of
heart"!

73,

Bill Henry,

K9GWT

HAL
PRODUCTS TIMELINE - Historical Reference This list is current as of
2013 - For Historical Reference
ONLY!

RTTY
TUs starting in the 1960s
Also Modems and Terminals for the Deaf and Hard of Hearing
CLICK THE IMAGE ABOVE TO READ ABOUT ESSCO...

(Wayne Green Editor or ARTS had his mother help
illustrate!

Let Play.... NAME THAT TU! (or
it's designer!)

Had a nice visit with Larry -
W0OGH and he turned us onto this
TU it hooks to the IF of a recv.

Can we find who designed it or
where it appears in a journal or...

Maybe it is just a ONE OFF..
but it is neat! Any hints appreciated!

And many thanks for the
addition to the TU collection Larry!

Ed Sharpe archivist for SMECC -
KF7RWW

RTTY
TU?SMECC has this at the museum.... WHO
MADE IT?!

Jim Haynes talk on the
question which is
better the ST-8000 or the Dovetron TU?

The ones with CRT displays are, I think, pretty rare. It's my
understanding that a time came when CRTs were impossible to get at
any reasonable price, so they went to the LED displays.

There seem to be many variations of the black faced model with LED
display. Some have the regenerator/speed converter, some have
Baudot-to-ASCII converters, some have 60ma loop and some don't,
some have everything on the main board and others have additional
board piggy-backed on the main board.

The Dovetrons seem to have got poor ratings from some users.

I have only one, and found a construction error on a PC board that
makes
it perform much worse than it should. But I haven't yet compared
it with
any of the others I have after fixing the error.

The original design of the MPC (multi path corrector) is I believe
what
is embodied in Hank Scharfe's patent 4,013,965. But apparently
that
did not perform well, because later models have all that stuff
pulled off
the PC board and there is a plug-in daughter board with a
"binary bit
processor" of some complexity. But apparently that didn't
work well
either, so there is a later version of the binary bit processor
that is
just a threshold corrector. The earlier ones detected mark and
space
separately and tried to deal with multipath echoes where mark and
space
signals are both present simultaneously. This last one simply
combined
the detector outputs with a threshold corrector and doesn't treat
the
signals separately after that point.

So it would be good if you could keep a selection of them with
these
different modifications and run them in parallel to see how they
stack up against one another.

In the HAL ST-8000 which is generally regarded as the best of the
hardware demodulators there is a multipath handling circuit, but I
don't know how effective it is. They detect mark and space
separately.
When the two detectors agree, that it is either mark or space,
that is
what it puts out. When the two detectors disagree it might be that
it is neither mark nor space, or that it is mark and space at the
same
time. Then they set a latch that preserves the last known-good
signal.

This could be considered hysteresis - the signal is held at
whatever was
good until the opposite condition is considered good. The Sprague
paper
back in 1944 advocated hysteresis for limiter-discriminator
demodulation,
but I haven't seen anything about how effective or useful it
really is.
And some hysteresis is added by putting the signal through a
low-pass
filter before making the mark/space decision.

One published amateur design incorporated anticipation, the
opposite of
hysteresis. As soon as he saw mark going away he flipped the
output to
space, and vice versa. It would be interesting to build a
demodulator
with a switch giving no hysteresis, hysteresis, and anticipation
and
see which performs better under various conditions.

There is presumably a government specification somewhere which led
to
the development of similar demodulators by several different
companies.
Dovetron, HAL ST-8000 and Electrocom 440 series all have
independently
tunable mark and space frequencies, achieved by different means,
and
MIL-STD-188 output instead of loop current, and other
similarities.
And the Frederick 1280.

The outstanding feature of the Dovetron is that, while the
frequency
calibration of the knobs is only approximate, it's very easy to
tune in
a signal of arbitrary shift. As I recall the ST-8000 (I haven't
had
one in my hands) is rather harder to tune. The Electrocom has two
options - one lets you set the frequency and the shift by separate
knobs,
and the other lets you set the two frequencies by separate knobs.
But
the way the tuning indicator works it is very hard to tune in
signals
with the knobs. And the Frederick has you enter the mark and space
frequencies on a keypad.

Someone suggested that the real purpose of these things is to tune
in
one channel of a frequency division multiplex carrier system. In
that
case the frequencies are pretty well known and stable, unlike
random
FSK RF signals, so the tuning indicator needs to show you only
that you
are or are not in tune, not how to get in tune. The old
crossed-ellipses
CRT display has the virtune that you can see which direction you
are off
frequency and tune the receiver to correct it. Zero-center meter
displays
are not very helpful since the average of typical FSK signals is
not zero.

I'll put in an aside here. Some WW-II military stuff, like the
BE-77 line
unit has a zero center meter and you do adjust for a zero reading
while
receiving repeated space-bar characters. This signal doesn't have
a zero
average at all, but the meter is intentionally biased to read zero
on
specifically that signal.

I've always wondered why somebody didn't do a peak-reading
zero-center
meter so that correct tuning would give a zero reading. (The
average of
the peaks would be zero even if the average of the signal isn't.)

Another good one is in the amateur PK-232 and some other amateur
equipment
where a single LED bar indicates mark and one end and space at the
other,
so you just tune to center the brightest spots on the LED.

The Electrocom 440 series has a CRT tuning indicator, but it's
practically
useless because they multiply the deflection signal by the
detector
output. So you get either a vertical bar or a horizontal bar or
nothing,
which doesn't tell you which direction you are off frequency. I've
got
a modification in mind that would make the display more
conventional and
useful, but I haven't tried it yet - just bypass the multipliers
and
display the filter outputs. The Frederick 1280 has parallel
vertical
bar graphs for the mark and space. That's no worse, I guess, than
the
crossed LEDs of Doveton and later HAL, but it's not very easy to
tune.

Now I bet that's more than you wanted to know.

jhhaynes at earthlink dot net

Everyday we rescue items you
see on these pages!
What do you have hiding in a closet or garage?
What could you add to the museum displays or the library?